Wrightbus: Recruitment freeze at County Antrim company
The County Antrim manufacturer, behind the so-called Boris bus, is imposing a recruitment freeze "with immediate effect".
A company memo states Wrightbus is finalising changes to its "organisational structure".
It said this was in response to "challenges in both the local and overseas markets".
Wrightbus employs more than 1,500 people, mainly in Ballymena.
The company is best-known for manufacturing the London Routemaster Bus championed by Boris Johnson.
Earlier this year, a Routemaster order worth £62m was confirmed.
The company memo, seen by the BBC, states the freeze will apply to "all recruitment", including vacancies currently open. It said no offers of employment should be made without "exceptional business need".
The letter added that the changes, which will reduce operating costs, will be communicated to staff in coming weeks.
The company said it had no comment to make but it is understood the move is about maintaining competitiveness rather than dealing with any particular issue.
The group's last financial figures, for 2014, showed it made an annual profit of £14.5m on a turnover of £297m.